Principles of Sensory Systems

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Psy 111 Basic concepts in Biopsychology Lecture
9 Hearing
Website http//mentor.lscf.ucsb.edu/course/fall/p
syc111/
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Objectives

• Describe the nature and properties of sound.
• Identify the route of sound to the ear and where
  transduction occurs.
• Explain the organization of the cochlea and the
  organ of corti.
• Describe the transduction of sound waves and the
  maintenance of sound properties.
• Describe the output pathway from the ear to the
  cortex and how sound properties of encoded.
• Identify the transducers for the vestibular
  system and related circuitry
• Introduce language localization in the brain as a
  higher-order association area describe its
  laterization.

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Sensory systems
getting info encoded in the primary sensory
cortex

• Principles of sensory systems
• Chemical sensory systems
• Vision the photic sensory system
• Hearing (Touch) the mechanical sensory systems

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Principles of Sensory Systems
Transduction Mechanism - envirnomental energy -gt
biological energy Relay Centers series of
projection neurons Topographically arranged
shape of information is maintained Parallel
Pathways quality of information is maintained
Cross Midline it just does Hierarchical
organization convergence at relays to cortex
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Sound Waves Air Compression
Sound waves compressions in air produced by
vibrations
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Properties of Sound Waves
Frequency pitch Human range is 20 20K Hz
Intensity loudness
Real sounds are complex mixtures of frequencies
intensities
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Properties of Sound Waves
Real sounds are a mixture of waves with different
amplitudes and frequencies which give complexity
to hearing.
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Structure of the Ear
Outer ear serves to focus sound waves and
involved in localization of sound
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The Middle Ear
Middle ear serves to transfer air compressions
(of the outer ear) to fluid compressions (of the
cochlea). This process also greater amplifies
force of wave.
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Middle Ear Muscle Attentuation Reflex
Muscles contract in response to high intensity
sounds to protect ear from low frequency sound
damage.
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The Inner Ear
Cochlea comprises 3 interconnected tubes
(scalae) and the organ of Corti
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Functional Anatomy of the Cochlea
Cochlea is a pressure-conducting, cone-shaped
tube from the Oval to Round windows
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Wave formation and Resonance
Air pressure on the Tympanic membrane causes
movement of the middle ear with the Stapes
causing vibration of the Oval window resulting in
fluid waves within the Cochlea. Waves resonate at
specific point on the (flexible) Basilar
membrane. Waves dissipate at Round Window.
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Frequency Encoding
Point of resonance is determined by frequency of
sound wave, providing a basis for anatomical
encoding of pitch. i.e. more displacement/mechanic
al force at a point will produce more
transduction
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Organ of Corti
Scala tympani
The organ of Corti lies between the (flexible)
basilar membrane and the (rigid) tectorial
membrane
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The organ of Corti and cochlear waves
Waves move the basilar membrane but not the
tectorial membrane resulting in conformational
changes in the stereocilia of hair cells.
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Depolarization of hair cells
Movement of basilar membrane changes conformation
of stereocilia resulting in increased K
conductance. Endolymph has usually high
K. Thus. increased K conductance depolarizes
cell, opening vg-Ca channels, and increases
transmitter release.
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Hair Cell Potentials
Increased sound pressure (louder noise) produces
higher graded receptor potentials
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Hair cell synapses
There are more Outer hair cells than Inner hair
cells but Inner hair cells account for the
majority of inputs to the Spiral gangalion cells
(primary afferent neurons).
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Amplification by Outer Hair Cells
Outer hair cells have motors that serve to
amplify sound waves using the wave
energy. Cochlear Amplifier
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Intensity encoding-at same frequency
Sound intensity (loudness) corresponds to height
of wave. Higher waves spread out more along
basilar membrane.
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Frequency tuning of auditory neurons

• Neurons respond maximally to characteristic
  frequencies.
• Higher characteristic frequencies correspond to
  higher APs.

Population encoding is similar to in other senses
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Tonotopic mapping
Spatial location encodes (intermediate to high)
frequencies
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Central Auditory Pathways
Spiral ganglion cells synapse on complex brain
stem circuits that precede thalamic relay to the
cortex. Brain stem circuits involved in auditory
activated reflexes.
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Summary of Auditory Pathways

• Auditory nerve axons
• (Ipsilateral) cochlear nucleus
• Superior olives (bilateral connections sound
  localization)
• Inferior colliculi (involved in orienting)
• Medial geniculate nucleus
• Primary auditory cortex

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Auditory Cortex

• 2 - 3 areas of primary auditory cortex
• About 7 areas of secondary
• Tonotopic organization (encodes frequency)
• Functional columns (cells of a column respond to
  the same frequency)
• Secondary areas do not
• respond well to pure tones
• and have not been
• well-researched

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Auditory vs Visual Systems
thalamus
Brain stem neurons perform early (pre-thalamic)
processing of auditory info as the retina does
for visual info.
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The vestibular system
The labyrinth contains the receptor cells for
the vestibular system.
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Vestibular system activation
Head movement activates the hair cells of the
vestibular system. Transduction is similar to
auditory system except environmental signal is
produced by orientation of the body relative to
gravity.
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Vestibular system outputs
Vestibular system has afferents to many motor
sites causing diverse actions which produce
subconscious actions.
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Auditory and Visual Association Areas in Language
Perception
Motor side of language covered later.
Dorsal Stream (processes attributes)
Visual cortex

• Specialized for language perception
• Identified in neuropsychology exams.
• Receives complex /high level auditory and visual
  inputs.
• Assymmetrically localized on left side of brain.

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Auditory and Visual Association Areas in Language
Perception
Paralyze right side of brain no langauge
loss Paralyze left side of brain severe
langauge loss (96 in right-handed 70 in
left-handed)
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Hemispheres of Split-Brain Patients Function
Independently

• Left hemisphere can tell what it has seen, right
  hemisphere can show it.
• Studies of split-brain patients
• Present a picture to the right visual field (left
  brain)
• Left hemisphere can tell you what it was
  (verbally)
• Right hand can show you, left hand cant
• Present a picture to the left visual field (right
  brain)
• Subject will report that they do not know what it
  was
• Left hand can show you what it was, right cant

Both hemispheres have some language abilities
Left is usually dominant for verbal ability.